1. Field of the Invention
The present invention relates to phosphorescent fibers with a high degree of luminescence and a method for manufacturing the same. More particularly, the present invention relates to the encapsulation of phosphorescent particles, thereby enabling large-size phosphorescent particles of irregular shapes to be used without problems.
2. Description of the Prior Art
Recently, phosphorescent materials have found applications in various fields, including clocks, electronic appliances, decorative finish, marks, fire safety equipments, illuminators, fashion products, toys, and cloths and textile products.
The cloths and textile products having luminescent properties are usually coated with phosphorescent pigments. Alternatively, synthetic fibers are spray-coated with phosphorescent pigments to provide luminescent properties to cloths and textile products. After being worn or washed, the cloths or textile products prepared in these coating methods, however, strongly tend to be deprived of the phosphorescent pigments coated. Further, such products are low in afterglow brightness level and short in an afterglow extinction time.
Another method for providing luminescence to cloths or textile products is to prepare fibers from phosphorescent pigment-added synthetic resins. This method also fails to overcome the problems of a short afterglow extinction time and low afterglow brightness. Another disadvantage of this method is that a relatively large amount of phosphorescent pigment is required, causing economic burden and making the mechanical properties of the fibers poor.
ZnSiCu-based phosphorescent pigments, which commonly are used, are problematic in practical uses because the afterglow brightness is low and the length of time for which the fiber is luminescent is short. According to these results, a relatively large amount of pigment is needed to provide satisfactory luminescent properties to fiber. Also, ZnSiCu-based phosphorescent pigments are not applied to cloths and textile products because of their being poor in chemical stability, light fastness and weathering resistance.
U.S. Pat. No. 5,914,076, yielded to Marc Schloss et al., discloses a phosphorescent fiber with a high degree of luminescence. To obtain this fiber, first, flow agent particles, aluminum oxide C, are blended with metal oxide phosphor particles in an amount less than or equal to 2% by weight of the phosphor particles. The blended particles are finely sifted through a 10 microns screen, in a sonic-sifting apparatus. The sifted particles are introduced into a carrier resin, consisting of thermoplastic polymers such as polyamide, polyester, and polypropylene, during the melt-stage of an extrusion and pelletizing process, to form pellets in an amount of less than or equal to 30% by weight of the polymer. From the pellets, phosphorescent textile yarn is formed in an amount of less than or equal to 10% by volume of the polymer.
This fiber is advantageous in that the spinning process can be uniformly carried out with a reduction in problems including yarn cutting because the phosphorescent particles are uniformly globular with a small particle size. This fiber is, however, significantly poor in luminescent properties, the most important characteristic. To avoid this problem, the amount of the phosphorescent pigment may be increased but, in this case, the yarn cutting as well as the production cost increases.
The relationship between particle size and after glow strength of phosphorescent particles is shown in Tables 1 and 2, below. This data was obtained by exposing two types of phosphorescent particles with average particle sizes of 42 xcexcm and 9 xcexcm, respectively, to a commercial light source 4001xc3x97D65 for 20 minutes and measuring their afterglow brightness (light density) by use of a color luminance meter, such as that manufactured by Topcon, identified as BM-5A (angle of measurement 2, measuring lens 3). As can be seen in Tables 1 and 2, the phosphorescent particles with average particle sizes of 42 xcexcm and 9 xcexcm were found to have an afterglow brightness of 1890 mcd/m2 and 1097 mcd/m2 at 1 min after exposure, respectively. The smaller particles are calculated as having only 58% the afterglow brightness of the larger ones. The reduction in afterglow brightness of phosphorescent particles occurs at the same rate for both particle sizes. Thus, smaller phosphorescent particles show weaker initial brightness levels and suffer from quicker disappearance of afterglow brightness, so that they are less desirable to apply to phosphorescent synthetic fibers.
Therefore, there is no choice but to increase the content of phosphorescent particles in order to improve the luminescent properties if the particle size is not changed. However, if they are used in a large amount, phosphorescent pigment, although being uniform in morphology and small in size, caused yarn cutting and damage of equipments. Additionally, a large amount of phosphorescent particles experience difficulty in being dispersed with synthetic resins, so that uniform luminescent properties cannot be affected throughout the phosphorescent fibers prepared therefrom. Further, a large amount of phosphorescent particles give rise to an increase in the production cost.
U.S. Pat. No. 5,674,437, yielded to Richard H. Geisel et al., discloses a process for providing luminescence for fibrous material by mixing metal aluminate oxide pigment with thermoplastic resins and melt extruding the mixture into a fibrous phase. Also, Richard H. Geisel et al., report that a fiber comprising 9.1% by weight of metal aluminate oxide pigment exhibits a light density of over 1000 mcd/m2 after one minute and shows a light density of approximately 100 mcd/m2 after approximately 80 minutes. According to the above tables 1 and 2, however, it is impossible to obtain the above results because a luminescent fiber produced by Richard H. Geisel et al. contains metal aluminate oxide pigment in which particle size of the metal aluminate oxide pigment is from 12 to 21 microns. The picture of the phosphorescent fibers comprising about 9% by weight of phosphorescent pigment with an average particle size of 42 xcexcm and 19 xcexcm, respectively, is shown in FIG. 1. Phosphorescent fibers containing phosphorescent pigment with an average particle size of 42 xcexcm and 19 xcexcm show a light density of 900 mcd/m2 and 650 mcd/m2 after one minute, respectively.
U.S. Pat. No. 5,686,022, yielded to Yoshihiko Murayama et al., refers to a phosphorescent phosphor represented by M1xe2x88x92xAl2O4xe2x88x92x wherein x is not zero and M is selected from the group consisting of calcium, strontium, barium, and mixtures thereof, comprising europium as an activator and a metal as a co-activator selected from cerium, praseodymium, neodymium, thulium, terbium, dysprosium, holmium, erbium and mixtures thereof. Nowhere is mentioned the application of the phosphorescent phosphor to fibers.
Accordingly, it is an object of the present invention to provide a phosphorescent fiber, which can show longer-lasting, high, uniform luminescence there throughout.
It is another object of the present invention to provide a phosphorescent fiber, which is superior in light fastness and weathering resistance.
It is still a further object of the present invention to provide a phosphorescent fiber, which has such excellent physical properties as to be applicable to various textile products.
It is still another object of the present invention to provide a method for manufacturing a phosphorescent fiber, by which phosphorescent particles, with an average particle size of 42 xcexcm and a size distribution of 10-60 xcexcm, can be used while apparatuses such as spinnerets can be operated at constant spinning conditions with minimal damage and no yarn cutting.